Water dispersible nonwoven fabric

ABSTRACT

A WATER DISPERSIBLE NONWOVEN FABRIC COMPRISING A LAYER OF OVERLAPPING, INTERSECTING FIBERS BONDED WITH A WATER INSOLUBLE, SUBSTANTIALLY WATER INSENSITIVE, FILM-FORMING, NONSELF-CROSSLINKING POLYMER CONTAINING A WATER SOLUBLE MATERIAL HAVING PSEUDO-PLASTIC FLOW PROPERTIES UNIFORMLY DISTRIBUTED THROUGHOUT THE POLYMER.

Jan. 12, 1971 1 M. R. FECHILLAS WATER DISPERSIBLE NONWOVEN FABRIC FiledOct. 9, 1968 INVENTOR Mo /454 A. F5070; 445

. BY fly a a, 1A

ATTO NEY United States Patent ABSTRACT OF THE DISCLOSURE A waterdispersible nonwoven fabric comprising a layer of overlapping,intersecting fibers bonded with a water insoluble, substantially waterinsensitive, film-forming, nonself-crosslinking polymer containing awater soluble material having pseudo-plastic flow properties uniformlydistributed throughout the polymer.

This invention relates to a new nonwoven fabric which is readilydispersible in water and is flushable.

Nonwoven fabrics have gained wide acceptance in disposable areas such assanitary napkins, diapers, bandages, etc. A major problem with thesedisposable products has been the manner of disposing. One technique fordisposing is incineration; however, this cannot always be done and inmany instances, depending upon the fibers used and binders used theproblems of burning are greatly increased. Furthermore, it is difiicultto burn such products in the homev and if such products have been usedin various medical end uses there are even further problems of burningwith regard to contamination. Most of these nonwoven fabrics require wetstrength so that they will be functional during many of their end usesand hence, they are not readily flushable down home water closets orindustrial sewer systems as they will readily plug sewers and septicsystems.

I have now discovered a bonded nonwoven fabric which has good strengthwhen dry, reasonable strength in the presence of most body fluids, suchas urine, blood, menstrual fluid, etc., yet is readily dispersible inwater and may be flushed in the home water closets and disposed instandard sewer systems or septic systems.

My improved fabric comprises a layer of overlapping, intersecting fibersand from about 4 percent to about 35 percent by weight of fabric ofbinder distributed in the fiber layer. My binder comprises from about 70percent to about 90 percent of a water insolu'ble, substantially waterinsensitive, film-forming, nonself-crosslinking polymer. Uniformlydistributed throughout the polymer is a water soluble material havingpseudo-plastic flow properties.

In use, the fabric has good dry strength depending upon the amount ofbinder applied to the fabric and the manner in which it is applied yetwhen placed in water the soluble portion of the binder is dissolved anddisrupts the globules of binder into very small globules which readilyallow the fibers to disperse and the fabric to be flushed. Thedissolving out of the water soluble portion of the binder prevents thebinder from adhering to itself and to other fibers and greatly reducesthe strength of the fabric and allows the fibers to be readily dispersedwith little, if any, agitation.

The invention will be more fully described in conjunction with thefollowing drawings wherein:

FIG. 1 is a plan view of a bonded nonwoven fabric in accordance with thepresent invention;

FIG. 2 is a greatly enlarged cross-sectional view taken along line 22 ofFIG. 1;

FIG. 3 is another embodiment of a water dispersible nonwoven fabric inaccordance with the present invention.

Referring to the drawings in FIGS. 1 and 2 there is shown the waterdispersible nonwoven fabric 10. The

3,554,788 Patented Jan. 12, 1971 ice fabric comprises a layer ofoverlapping, intersecting, textile length fibers 11 and substantiallyuniformly distributed throughout this fibrous layer are globules ofbinder 12.. As is more clearly shown in FIG. 2 these globules of bindercomprise for the most part a material 15 which is not water sensitivebut adheres readily to the fibers 16. This material is a waterinsoluble, film-forming, nonselfcrosslinking polymer. Uniformlydistributed throughout this material is a water soluble material 17.

In FIG. 3 there is shown a nonwoven fabric 20 comprising a layer ofoverlapping, intersecting, textile fibers 21 with a binder distributedin a predetermined pattern 22 over this layer, the pattern being aseries of horizontal wavy lines. The binder comprises anonself-crosslinking polymer '23 which is not water sensitive anduniformly distributed throughout the binder areas is a water solublematerial 2.4.

The base layers suitable for conversion into the fabric of the presentinvention may 'be formed by carding, garnetting, air deposition, waterdeposition and any of the various techniques known in the art. Thefibers in the layer may be oriented predominantly in one direction as ina card web or a card Web laminate or they may be substantiaillyisotropic, that is, have equivalent strength in all directions ifdesired. For napkin covering and similar types of uses such as a facingon disposable diapers where the fabric is to be flushable the web isfairly thin and should weigh between to 400 grains per square yard.

Uniform fiber distribution is an important characteristic particularlyin fabrics which must possess a substantial amount of strength, and befree of weak spots due to lack of uniformity. 'Uniform webs may lbeproduced by carding in which case it is advantageous to use fibers whichhave good carding characteristics and can be blended into a uniformcarded web with facility. Fibers of viscose rayon and cotton are bothsatisfactory in this respect. However, it should be understood thatalmost any kind of textile fiber may be employed in forming fabrics ofthis invention depending upon the intended end use. For instance, thebase layer may comprise natural fibers such as cotton, jute, or wool.Artificial fibers of viscose rayon, cuprammonium, cellulose acetate,etc., or synthetic fibers such as polyesters, polyamides, polyolefins,etc., alone or in combination with one another.

The length of the fiber is also important in producing the fabrics ofthe present invention. The length should usually be a minimum of inch inorder to produce uniform webs in the carding operation and it ispreferred that the length be 1 /2 inches or less so that the fibers willnot rope when they are dispersed in water. It has been found that fibershaving a length of greater than 2 inches when placed in the fabric,though the fibers will disperse and separate in water, their lengthtends to form ropes of fibers which is undesirable when flushing in homewater closets.

The binder may be deposited on the layer by printing, spraying,impregnating or by other techniques wherein the amount of binder may bemetered and the binder can be distributed uniformly throughout the web.The binder may be applied over the entire surface of the layer or it maybe distributed in a multiplicity of small closely spaced areas. Thebinder may be distributed in lines running across the width or at anangle to the width of the web or in separate small shaped areas havingcircular, angular, square, or triangular configurations. It is preferredthat when the binder is applied to the fibrous layer there be leftunbonded areas in the layer. These unbonded areas of fibers readilyabsorb water which attacks the binder areas and makes the fabricdispersible in shorter periods of time.

The amount of binder applied should be from about 4 to 35 percent byweight of the fabric. If less than this amount of binder is applied thefabric does not have sufficient strength; whereas, if more than thisamount of binder is applied the fabric will not have suitable waterdispersibility and be readily fiushable in the home water closet and maylose desirable properties of softness and absorbency. It is preferredthat the amount of binder be between about 4 to 12 percent by weight ofthe fabric in order to produce very quick water dispersibility.

The binder utilized in producing the nonwoven fabric of the presentinvention comprises two parts; a water soluble part and a waterinsoluble substantially water insensitive part. The binder shouldcontain from about to percent of the water soluble portion. Minimumamounts of other chemicals such as antifoaming agents, fire retardants,colors, etc., may also be added to the binder.

The water insoluble portion of the binder must be substantially waterinsensitive. By water insensitivity it is meant that films of the binderdo not readily blush and have very little, if any, wettability. Ameasure of the wettability or water insensitivity of the polymer is thecontact angle which is a measure of the surface energy required todisperse a drop of water on the polymer surface. Hence, the higher thecontact angle the more wettable or water sensitive the polymer and thelower the contact angle the more water insensitive the polymer.

There are a number of techniques for measuring the contact angle whichmay be used. One such technique is to clean the surface of the film madefrom the polymer to be tested with various materials such as deionizedwater or organic cleaners and then drying the film. Static is removedfrom the film and the film placed on the platform of an instrument knownas a contact angle goniometer. The contact angle goniometer consists ofa microscope mounted with its axis horizontal and equipped with aspecimen block which can be raised or lowered and moved from side toside. The normal eye piece of the microscope is replaced with aprotractor eye piece divided into degrees on a rotating scale with avernier in minutes on a fixed arm. The cross hairs in the eye piecedivide the field view into quadrants. A drop of deionized water ispushed onto the film from a capillary dropper mounted above the specimenblock. The dropper is an ordinery eye dropper with the tip drawn into aone inch capillary with a diameter just small enough to prevent waterfrom running out of the tube under gravitational force only. To assistin dispersing the water from the dropper the tip of the capillary isground at an angle to the perpendicular. The protractor scale is thenrevolved until its cross hair is parallel to the surface on which thedrop is resting. The other cross hair is adjusted until it is tangent tothe drop at the point of contact with the Surface on which it isresting. The angle between the cross hairs inside the drop is read fromthe protracting scale. This is the advancing contact angle. Using thedropper, water is subtracted from the drop on the sample and thereceding contact angle is recorded. Due to water evaporation theseangles may change and, hence, for the purposes herein all references tocontact angles are to angles which are taken instantaneously, that is,as soon as the water is placed on the film the angle is measured andthen the water removed.

Another technique for measuring contact angles is to place the water onthe film and take a cross-sectional picture of the film with the waterthereon, enlarge this a suitable number of times, and then measure thecontact angle mechanically. The contact angle is the sum of theadvancing and receding angles divided by two.

In accordance with the present invention the water insoluble portion ofthe binder must have a contact angle from about to 70 and preferablyfrom about to If the contact angle is greater than that portion of thebinder will be too water sensitive and, hence, will not provide suitablestrength in the final fabric; whereas, if the contact angle is less than50 the binder 4 is too water insensitive and, hence, will not produce awater dispersible fabric in accordance with the present invention.

In accordance with the present invention the water insoluble portion ofthe binder must have a degree of wettability such that the contact anglewith water on a cast film of such a polymer is between 50 to 70.

It is believed that the contact angle of the polymer may be greatlycontrolled by the surfactant used in the polymerization of the polymer.Many of the binder polymers are polymerized in emulsion form, what istermed emulsion polymerization, and in so doing generally varioussurfactants or soaps are added to aid this polymerization. It isbelieved that the more surfactant present the more wettable or the lesswater insensitive the polymer would be. In some instances polymers arepolymerized in the presence of a protective colloid such as polyvinylalcohol rather than surfactants and such polymers make very suitablewater insoluble binder portions in the present invention.

The water insoluble binder portion must also be filmforming. Byfilm-forming it is meant that particles of the polymer have the abilityto cohere and form a continuous phase at room temperature.

The water insoluble portion of the binder also must benonself-crosslinking. By nonself-crosslinking it is meant that there areno free radicals or functional groups on the polymer which willcrosslink with themselves at elevated temperatures.

Examples of suitable water insoluble, substantially water insensitive,film-forming, nonself-crosslinking polymers are the acrylic resinsespecially the vinyl acrylic resins, the acetate resins and thebutadiene styrene polymers.

The water sensitive or water soluble portion of the binder may be any ofthe various water sensitive binders such as hydroxyethyl cellulose,carboxymethyl cellulose, the natural gums such as guar and preferablythe alginates such as sodium alginate. The important thing is that therebe from about 10 to 30 percent of the water soluble material in thebinder in the final fabric and that this water soluble material will besubstantially uniformly distributed throughout the binder. The preferredamount of water soluble material is from 12 to 26 percent with the mostpreferable amount being 14 to 18 percent. If too little, that is lessthan 10 percent water soluble material is used, the fabric Will not bewater dispersible, whereas if too much water soluble material is usedthe fabric will not have sufiicient dry strength for most end uses.Also, if the water soluble material is not uniformly distributedthroughout the resin polymer globule or binder portion when it isdissolved out it will not sufficiently disrupt the fabric and allowseparation of fibers to make the fabric dispersible. The uniformdistribution of water soluble material through the binder isaccomplished by adding the water soluble material to the resin emulsionprior to applying the binder to the fabric. By water soluble material itis meant that the material actually undergoes a physical change whenplaced in water in that the water gets inbetween the molecules andbreaks up material and that substantially all proportions of materialare dissolvable in water.

The water soluble materials useful in the present invention havepseudo-plastic flow properties and not Newtonian or thixotropic flowcharacteristics. By pseudoplastic it is meant that the flow ischaracterized in that its rate of shear is not proportional to theshearing force but actually that its rate of shear increases in lessproportion to the shearing force applied. Another way of saying this isthat viscosity increases in less proportion to the shearing force.Suitable psuedo-plastic water soluble materials have viscosities of fromabout 500 to 2,000 centipoises and preferably from about 800 to 1,400centipoises. The most suitable water soluble materials have viscositiesof between 1,100 and 1,200 centipoises.

The most preferable water soluble material useful in the presentinvention is a polymer of mannuronic acid and gluronic acid orderivatives of these materials and specifically sodium alginate.

The following example is illustrative of one fabric according to thepresent invention:

EXAMPLE A fibrous layer of 1% inch, 1% denier extra dull viscose rayonweighing about 252 grains per square yard is formed from standardcarding machines. A binder having the following formulation is formed:

Pounds Sodium alginate 2.25 Nonself-crosslinking water insensitive vinylacrylic polymer (contact angle about 5860) 12.5 Antifoaming agent 0.2

Water 85.25

The pH of this binder formulation is brought to 7.0 with the addition ofammonia. This binder formulation is printed onto the fibrous layer in apattern of horizontal wavy lines of six lines per inch. The amount ofbinder add-on is 12 grains per square yard.

The resultant fabric has a softness of about 72 and has a machine drytensile of about 4 pounds per inch of width and a cross directiontensile of about .3 pound per inch. A swatch of the fabric six inches bysix inches is placed in approximately 600 ml. of water and the waterhand stirred being careful not to touch the fabric. The fabric dispersesin approximately seconds and cannot be removed in a single piece or in aseries of pieces from the water.

' Having now described the invention in specific detail and exemplifiedthe manner in which it may be carried into practice it will be readilyapparent to those skilled in the art that innumerable variations,modifications, applications, and extensions may be made to the basicprinciples involved without departing from its spirit and scope. Itherefore intend to be limited only in accordance with the appendedclaims.

I claim:

1. A water dispersible, nonwoven fabric comprising a layer ofoverlapping, intersecting textile fibers, said fibers being from aboutinch to about 2 inches in length, and from about 4 to 35 percent byweight of the fabric of a binder distributed in said fabric, said bindercomprising from about 70 to 90 percent of a water insoluble,substantially water insensitive, nonself-crosslinking, filmformingpolymer and from about 10 to 30 percent of a water soluble materialhaving pseudo-plastic flow properties uniformly distributed throughoutsaid polymer, said water insoluble polymer having a contact angle offrom about 50 to 70, and said water soluble material having a viscosityof from about 500 to 2,000 centipoises.

2. A Water dispersible nonwoven fabric according to claim 1 wherein thewater insoluble polymer contains a polyvinyl alcohol protective colloid.

3. A water dispersible nonwoven fabric according to claim 1 wherein thewater insoluble polymer is a vinyl acrylic polymer.

4. A water dispersible nonwoven fabric according to claim 1 wherein thewater soluble material has viscosity from about 800 to 1,400centipoises.

5. A water dispersible nonwoven fabric according to claim 1 wherein thewater soluble material has a viscosity of from about 1,100 to 1,200centipoises.

6. A water dispersible nonwoven fabric according to claim 1 wherein thewater soluble material is a polymer of mannuronic and gluronic acids orderivatives thereof.

7. A water dispersible nonwoven fabric according to claim 1 wherein thewater soluble material is sodium alginate.

8. A water dispersible nonwoven fabric according to claim 1 wherein thefibers are viscose rayon fibers.

9. A water dispersible nonwoven fabric according to claim 1 wherein thefibers are textile fibers having a length of inch to 1% inches.

10. A water dispersible nonwoven fabric according to claim 1 wherein thebinder is distributed in a predetermined pattern over the surface of thefibrous layer.

11. A water dispersible nonwoven fabric according to claim 1 wherein thewater insensitive polymer has a contact angle of from 55 to and thewater soluble material has a viscosity of from 800 to 1,400 centipoises.

12. A water dispersible nonwoven fabric according to claim 1 wherein thewater insensitive polymer is a vinyl acrylic polymer and the watersoluble material is sodium alginate.

13. A water dispersible nonwoven fabric according to claim 1 wherein thefibers are viscose rayon fibers having a length of inch to 1% inches,the water insensitive polymer has a contact angle of from 55 to 65 andthe water soluble material has a viscosity of from 800 to 1,400centipoises.

14. A water dispersible nonwoven fabric according to claim 13 whereinthe binder is distributed in a predetermined pattern over the surface ofthe fiber layer.

15. A water dispersible nonwoven fabric according to claim 13 whereinthere is about 4 to 12 percent binder by weight of the fabric.

16. A water dispersible nonwoven fabric according to claim 13 whereinfrom about 14 to 18 percent of the binder is water soluble material.

References Cited UNITED STATES PATENTS 2,905,568 9/1959 Burgeni 117-1403,009,822 11/1961 Drelich et a1 161-146 3,122,447 2/1964 Sexsmith117-140 3,123,075 3/1964 Stamberger 128-287 3,310,454 3/1967 Florio etal 161-146 3,480,016 11/ 1969 Costanza 161-156 ROBERT F. BURNETT,Primary Examiner J. J. BELL, Assistant Examiner U.S. Cl. X.R.

